Effect of the reduction of nutrient solution concentration on leafy vegetables quality grown in floating system

The greenhouse production has been evolving more and more towards sustainable or environmental friendly systems. However, the yield and the quality of vegetables must be preserved. The reduction of fertilisers should be obtained without compromising the marketable produce. Floating systems for minimally leafy vegetables production have been increasing, but adequate nutrient solution concentrations are not yet available. Usually growers use standard Hoagland’s solution even for short vegetable production cycle such as 20-40 days after sowing (depending from the period of year). The aim of our work was to identify the nutrient solution concentration range that allows to grow leafy vegetables without compromising the yield and the quality. Experiments were performed on lettuce (Lactuca sativa L.), rocket (Diplotaxis tenuifolia L.), spinach (Spinacia oleracea L.), lamb’s lettuce (Valerianella locusta [L.] Laterr.). These species were grown in floating system with standard nutrient solution (mM) 12 N-NO3, 3.8 N-NH4, 2.8 P, 8.4 K, 3.5 Ca, 1.4 Mg, 9.5 Na, 8.0 Cl, 2.7 S, 0.04 Fe and Hoagland’s concentration for micronutrients (NS100%), or with diluted nutrient solutions halved concentration (NS50%) or 1/4-fold (NS25%). At harvest, yield, total chlorophyll, carotenoids, total phenols and leaf nitrate content were determined. Results showed variability among species and cultivation periods. Slight differences in yield among the treatments were found, while significant differences were found in the different seasons. Total chlorophyll, carotenoids and phenols usually increased by increasing nutrient concentrations even if differences were not always significant. Leaf nitrates decreased in spinach with reduction of mineral concentrations in the nutrient solution, while in other species differences were not statistically significant.